The invention concerns the control of an automatic clutch in the drive train of a motor vehicle, having an engine controlled by the driver and a transmission shifted by the driver by actuating a lever. A motorized adjusting unit actuates the clutch. A system of sensors, which serves for controlling the adjusting unit, monitors the predetermined parameters and generates a signal for releasing the clutch if criteria are met for when a shift is intended by the driver, i.e. a change of transmission stage intended by the driver. In this arrangement, the system of sensors, in addition to the parameter of movement of the shifting element, also monitors a vehicle brake or its actuating element and a further parameter which can be influenced or controlled by the driver and releases the clutch if the movement of the shifting element or shift lever and the further parameter form a combination of parameters significant for intended shifting.
In motor vehicles having customary internal combustion engines, a transmission must be arranged in the drive train. The transmission allows the transmission ratio between the speed of the vehicle engine and the speed of the drive wheels to be changed according to the respective travelling speed and loading of the vehicle. In the case of customary transmissions, during a change of drive position the power flow between the engine and the drive wheels has to be interrupted by releasing a clutch.
It is known in principle to use automatic clutches for this purpose, i.e. the clutch is automatically released when changing a transmission stage and is subsequently re-engaged, (cf. for example German Patent document DE 35 05 586 A1).
U.S. Pat. No. 5,099,969 describes the problem wherein the speed of the vehicle engine may greatly increase to an undesired degree, i.e. the engine "races", if the automatic clutch is released every time the shifting element or shift lever is actuated. While the vehicle is being driven, the vehicle engine often operates at a higher torque because, to overcome the respective driving resistance, the gas pedal controlling the engine power is actuated with corresponding force. If in such an operating phase the shifting element or the shift lever is inadvertently actuated and this alone causes the clutch to be released, the engine working until then against the higher load can quickly reach extreme speeds on account of the diminishing load when the clutch is released. Therefore, according to U.S. Pat. No. 5,099,969 it is provided that, for clutch control, the torque of the engine or a parameter correlated with it is also monitored. So if there is an engine torque which exceeds a predetermined threshold value when the shifting element or shift lever is actuated, full release of the clutch is prevented. Rather, the transmissible clutch moment is merely reduced, so that the engine still has to work against a certain load. In this way, if the shifting element or shift lever is actuated inadvertently, for example if the shifting element or shift lever is actuated by strong vibration of the vehicle, racing of the engine is prevented.
According to U.S. Pat. No. 5,099,969, it is also envisaged to set the clutch to a limited transmissible moment when the vehicle is maintained stationary by the vehicle brake and the transmission is shifted to a drive position. This achieves the effect that the vehicle immediately tries to creep forward when the vehicle brake is released.
It is also known from German Patent document DE 32 00 919 A1 not to use the movement of the shifting element or shift lever as the sole criterion for intended shifting by the driver. This takes into account that many drivers often place their hand on the shifting element or shift lever without intending to shift the transmission. In such cases, the automatic clutch is to remain engaged as far as possible. For this reason, according to German Patent document DE 32 00 919 A1, it has been envisaged when detecting intended shifting to additionally monitor the torque generated by the engine or a parameter correlated with it, for example the position of the gas pedal or a throttle valve actuated by the latter in the intake system of an internal combustion engine of the vehicle. Intended shifting is only detected and a signal generated for releasing the automatic clutch if, on the one hand, the shifting element or shift lever is moved and, on the other hand, the engine torque lies below a predetermined low threshold value. This threshold value is set such that the gas pedal can virtually no longer be actuated.
The object of the invention is thus to increase reliability in the detection of intended shifting.
This object is achieved according to the invention by releasing the clutch independently of the at least one further parameter if the shifting element and the vehicle brake are actuated simultaneously.
The invention is based on the general idea of making the detection of intended shifting also possible if defects should happen to occur in the engine control or in the sensors or measuring pickups which serve to monitor the torque or the power of the engine. If, for example, the gas pedal should "stick" in the actuated position, the torque or the power of the vehicle engine may very well not fall below a predetermined threshold value. Nevertheless, the clutch is released if the vehicle brake and the lever are actuated. This takes into account the fact that, if there are engine control malfunctions, a driver will keep braking the vehicle and attempt to disengage the respectively selected drive position, at least whenever the engine power remains undesirably high.
Otherwise, with regard to preferred features of the invention, reference is made to the claims and the following explanation of the drawing, on the basis of which a particularly preferred embodiment is described.